The goal of this mixer design was to obtain fixed-tuned operation
around 345 GHz (280-370 GHz band). It is a single backshort waveguide
mixer. In the mixer block the waveguide height is reduced to a
quarter of the standard size. In this mixer two 1--square micron
connected seriesly Nb--Al oxide--Nb junctions, with RwC=6, have been
used. The individual inductive tuning elements are integrated with
the junctions. A new version of a non contacting backshort has been
developed for the reduced height waveguide mixer block. A magnetic
field is applied to the junctions in order to suppress the
Josephson current.
Measured mixer DSB noise temperature is 10 K (
level).
According to this data the mixer sensitivity may be estimated as one
photon.
During the test the mixer backshort, once fixed, remains in the optimal
position. For this backshort position the receiver exhibits a low
noise operation across the 
band.